Cathode for gas or vapor discharge tubes



July 16, 1940. E. F. LOWRY CATHODE FOB GAS OR VAPOR DISCHARGE TUBES Filed Nov. 10, 1937 Patented July 16, 1940 UNITED STATES oA'rnonE Foa GAS oa varoa mscmce roses Erwin F. Lowry, Batavia, Ill. Application November 10, 1937, Serial No. 173,885

23 Claims.

This invention relates to an improvement in gas or vapor discharge tubes, and more particularly to cathodes for use in gas or vapor tubes, such as are frequently used for rectiflers.

It has been known heretofore that thermionic cathodes for use in gas or vapor discharge tubes may be constructed so as to conserve the energy required to maintain them at a suitable elevated temperature, by folding the cathode ribbon to "10 form a cathode of considerably less area than that of the ribbon itself, as by corrugating and edgewinding it to helical form, as set forth in my prior patent, No. 1,968,608, granted July 31, 1934, on High efliciency oxide coated cathode and method of manufacture.

An object of the present invention is to improve the construction of the tube, primarily by improving the cathode structure, so that said cathode will have a maximum mechanical rigidity 20 with regard to deformation in any direction when supported only at its ends, and yet be of compact structure, with an envelope area much less than the area of the filament ribbon which forms it.

Another object of the invention is to provide a relatively large and uniform area of egress for electrons from the cathode by designing the oathode so that each and .every element of its area or surface is so located with respect to the exterior 30 of the structure as to promote ready egress of the electrons therefrom to the space surrounding said cathode.

These objects are accomplished primarily by constructing a thermionic cathode generally of 35 channel shape, which is then generated into the form of a helical coil, or other shape suitable for the purpose desired, forming a compact structure of appreciably less area than that of the filament ribbon.

In order to provide additional means of conserving the energy required to heat the cathode,

I enclose the helix described above within a cylindrical structure or shield which is closed also at the top, adjacent the anode, except for a small opening in the center of the top, but the bottom of said shield is open so as not to entirely close the active surface of the cathode.

A preferred embodiment of this invention, together with modifications thereof, is illustrated 50 in the accompanying drawing, in which:

Fig. 1 is a vertical sectional view of the cathode shield showing the cathode in place therein in elevation, taken substantially on the line l-l, of Fi 2;

Fig. 2 is a transverse sectional view therethrough, substantially on the line 2-2, of Fig. 1;

Fig. 3 is an enlarged cross-section of the channel of the cathode;

Fig. 4 is a similar view in which the channel is formed of substantial v-shape;

Fig. 5 is a similar view in which the cross-section of the channel is substantially rectangular with slightly rounded corners;

Fig. 6 is a plan view of a thermionic cathode, the channel of which is generated to form a coil -or flat spiral;

Fig. 7 is a side elevation of a cathode constructed substantially in the shape of a cone; and

Fig. 8 is a view partly in section and partly in elevation of a tube in which the cathode structure is used.

. Referring particularly to Figs. 1 and 2 of the drawing, the cathode I consists of a strip of material made of nickel, tungsten, or other metal suitable for the purpose. This cathode i preferably is formed of a filament ribbon which is shaped in any suitable manner into the form of a deep longitudinaltrough or channel, which channelshaped ribbon is then generated into suitable itlructural form, such as a helix, as illustrated in This helix is substantially enclosed, at least at its sides, within a shield having concentric cylinders 2 and an end plate 3, which closes the outer end of the shield and also the space around the cathode I, except for a small central opening 4 in said end wall. The shield extends beyond the helix in both directions and has the bottom end thereof substantially open to the space surrounding said shield. The end plate 3 has upturned peripheral edges secured rigidly to the innermost cylinder 2. The shield preferably is constructed of metal having good reflecting properties, such as nickel.

Due to the electrostatic shielding of the structure surrounding the cathode, it is sometimes diflicult to cause the discharge to start. To assist in the starting of the discharge, I prefer to coat the outside of the cap 3 with a thermionically active coating. When so coated, the cap acts as a pilot or starting cathode since it will emit sumcient electrons to incite the discharge as soon as it becomes heated by reason of conduction and radiation of heat from the filamentary'cathode to which it is directly attached.

One end of the cathode ribbon is secured to the underside of the end plate 3 of the shield, while the opposite end thereof is bent downward at 5 and is secured to a lead 6, which extends into the usual glass press 8 of the tube for support a rod 8, which extends between the cylinders 2 substantially to the upper end thereof, and also extends into the press 8, forming a lead for the other side of the cathode through the inner cylinder 2 and the end plate I which is connected directlywith the upper end of the cathode. The leads 6 and 9 are shown as connected respectively with the usual screw terminals I and II, adapted for screw connection with a socket in the usual manner of electric bulbs, although other forms of terminal connections may be used, if desired.

A getter tab I2 is secured on the rod 9, beneath the lower ends of the cylinders 2 whereby the getter material is evaporated into the cathode enclosure. The cylinders are supported on rods l3, secured therebetween and extending downwardly to a clamp l4 surrounding the press 8, to which clamp ll said rods l3 are afilxed for rigid mounting of the cathode structure in the tube IS. The cylinders 2 are held in spaced relation by the rods 9 and H which extend therebetween.

An anode I6 is connected through the usual seal with the end of the tube l opposite the terminals l0 and II, and is provided with an external terminal l1, forming a universal cap connection for the anode lead. The circuit in which the tube is used includes a connection from the terminal I l to the terminal I! for the anode I 6.

By forming the cathode I of channel shape, it will have a relatively large and uniform area of egress for electrons. In other words, the cathode is designed so that each and every element of its area and surface is so located with respect to the exterior of its structure so as to promote ready egress of electrons from the structure to the space surrounding the cathode.

01 Several variations in the form of the groove or channel of the cathode may be utilized, as shown in Figs. 3, 4 and 5, the form shown in Fig. 3, having a rounded bottom with substantially parallel sides, a modification of which is shown at l8 in Fig. 5, in which the bottom is substantially flat with corners slightly rounded, while a V-shaped channel is shown at IS in Fig, 4, the sides of which make an acute angle with each other. In these different forms, the greatest width of the channel preferably is less than the depth of the channel, for best results.

Other modifications in the cathode structure while retaining the channel shape are possible, such as the turning of the edges of the channel inwardly toward the axis of the helix, or the channel-shaped ribbon may be wound into a flat spiral, as indicated in at Fig. 6, or it may be formed into a generally conical shape, as shown at 2l-in Fig. '7, if desired, or the open side of the trough or channel may even be turned toward the open end of the cone instead of outwardly or inwardly.

The strip thus formed in any desired shape is self-supporting at its ends and possesses considerable rigidity against compression or expansion, the formation of the channel in the strip adding stiffness to the helix and resiliency.

After the cathode is formed, its major portion inside and outside, except the connected ends, is preferably coated with an electron emissive material, such as a mixture of carbonates of barium and strontium, which coating changes during the usual treatment of the tube to a mixture of the oxides of said metals.

After formation of the cathode and assembly 8,908,467 thereby. The shield is supported at one side by thereof in the shield, it is ready to be mounted in the tube l5, which is completed in the usual way with heating, Pumping, etc. A small quantity of mercury vapor or other ionizable gas, such as neon, argon, etc. is left in the tube when the pumping is finished in the usual manner of preparing mercury rectifier tubes.

In operation, the tube is connected in any suitable orusual rectifier circuit and current is connected with the terminals l0 and II. The anode I8 is connected through the. terminal II with the circuit to the source of current to be rectified. The lead 9 acts as the other connection to the rectifier circuit and care should be taken to maintain the correct phase relationship in making this connection.

The operation and function of the tube is substantially the same in efiect as that set forth in my prior patent, No. 1,968,608, granted July 31, 1934, and need not be described in further detail.

I claim:

1. A cathode for electrical discharge devices comprising a channel-shaped ribbon, substantially in the shape of an open coil having the convolutions thereof spaced apart.

2. A cathode for electrical discharge devices comprising a channel-shaped ribbon bent substantially into an open helix with the convolutions thereof spaced apart.

3. A cathode for electrical discharge devices comprising a channel-shaped ribbon bent substantially into an open heli with the convolutions thereof spaced apart and with the sides of said channel approximately normal to the axis of the helix.

4. A directly heated cathode for an electric discharge device comprising coiled ribbon coated throughout its major portion with electron emissive material, said ribbon having convolutions spaced apart and being formed doubled upon itself transversely in channel-shape with said channel extending lengthwise of the ribbon.

5. A cathode for an electric discharge device comprising a coiled ribbon, said ribbon having convolutions spaced apart and being formed doubled upon itself transversely in channelshape with said channel extending lengthwise of the ribbon with the open side of said channel turned outwardly from the axis of the cathode.

6. A cathode for an electric discharge device comprising a coiled ribbon, said ribbon having convolutions spaced apart and being formed doubled upon itself transversely in channelshape with said channel extending lengthwise of the ribbon with the open side of said channel turned outwardly from the axis of the cathode, and a radiation shield surrounding said ribbon comprising one or more coaxial cylinders having an end plate approximately closing one end thereof, said plate having an opening therein, and leads connected directly with the cylinder or cylinders and with an endof said ribbon.

7. In a tube of the character described, a filamentary cathode, a shield surrounding said cathode and comprising one or more concentric cylinders with an end plate substantially closing one end of said shield and the other end being open, said plate having an opening therein and being connected with an end of said cathode, and leads connected directly with the other end of the cathode and with the shield.

8. In a tube of the character described having an anode, a filamentary cathode comprising a longitudinally channel shaped ribbon wound in the form of a coil, a shield surrounding said cathode and comprising a plurality of concentric cylinders, and an end plate substantially closing one end only of said shield with the opposite end thereof open, said plate having an opening therein in the direction of the anode and being connected with an adjacent end of the cathode, a lead connected directly with the opposite end of the cathode, and a separate lead connected directly with one or more of said cylinders.

9. In a tube of the character described having an anode, a filamentary cathode comprising a longitudinally channel shaped ribbon wound in the form of a coil, a shield surrounding said cathode and-'comprising-a plurality of concentrio cylinders, and an end plate substantially closing one end only of said shield with the opposite end thereof open, said plate having an opening therein in the direction of the anode and being connected with an adjacent end of thecathode, a lead connected directly with the opposite end of the cathode, and a separate lead connected directly with one or more of said cylinders, the end plate being coated on its external surface with a thermionioally emissive coating.

10. In a discharge device of the character described, a cathode comprising a channel-shaped ribbon bent substantially into an opencoil with the convolutions thereof spaced apart approximately throughout its length, and means for supporting said coil at opposite ends thereof.

11. In a discharge device of the character described having an anode, a cathode comprising a channel-shaped ribbon bent substantially into an open coil with the convolutions thereof spaced apart approximately throughout its length, and means for supporting said coil onlyat opposite ends thereof.

12. In a discharge device of the character described having an anode, a cathode comprising a channel-shaped ribbon bent substantially into an open coil with the convolutions thereof spaced apart approximately throughout its length, said ribbon having the sides of the channel arranged approximately radially of the coil, and means for supporting said coil within the tube only at opposite ends thereof.

13. In a tube of the character described, an anode, a filamentary cathode comprising a longitudinally-channel shaped ribbon wound in the form of a coil, a shield surrounding said cathode and comprising one or more concentric cylinders and an end plate substantially closing one end of said shield, said plate having an opening therein and being connected with an adjacent end of said cathode, a lead connected with the opposite end of said cathode, and a separate lead connected with one of said cylinders.

14. In a tube of the character described, an anode, a filamentary cathode comprising a longitudinally-channel shaped ribbon wound in the form of a coil, a shield surrounding said cathode and comprising one or more concentric cylinders and an end plate substantially closing one end of said shield, said plate having an opening therein and being connected with an adjacent end of said cathode, a lead connected with the opposite end of said cathode, and a separate lead connected with one of said cylinders said cathode and the external surface of said end plate having a thermionioally emissive coating there- 15. In a tube of the character described, an anode, a filamentary cathode comprising a longitudinally-channel shaped ribbon wound in the form of a coil, a shield surrounding said cathode and comprising one or more concentric cylinders and an end plate substantially closing one end of said shield and being connected with an adjacent end of said cathode, a lead connected with the opposite end of said cathode, and a separate lead connected with one or more of said cylinders.

16. In a tube of the character described, an

' anode, a filamentary cathode comprising a longitudinally-channel shaped ribbon wound in the form of a coil, a shield surrounding said cathode= and comprising one or more concentric cylinders supporting an end of said cathode, a lead connected with the opposite end of said cathode, and a separate lead connected with one or more of said cylinders.

17. In a-discharge device of the character described, a cathode comprising a channel-shaped ribbon bentsubstantially into an open coil with the convolutions thereof spaced apart approxiimately throughout its length, and means for supporting said coil.

18. A cathode for an electrical discharge device comprising a ribbon channel-shaped in section transverse to its longitudinal axis, said channel-shaped ribbon being formed in the shape of a coil with the ends of each convolution thereof spaced apart.

19. A cathode for an electrical discharge device comprising a ribbon channel-shaped in section transverse to its longitudinal axis, said channel-shaped ribbon being formed in the shape of a helix with the convolutions thereof spaced apart.

20. A cathode for an electrical discharge device comprising'a ribbon channel-shaped in section transverse to its longitudinal axis, said channel-shaped ribbon being formed in the shape of acoil with the ends of each convolution thereof spaced apart, said ribbon being coated substantially throughout its length with an electron emissive material.

21. A cathode for an electrical discharge device comprising a ribbon channel-shaped in section transverse to its longitudinal axis, said channel-shaped ribbon being formed in the shape of a helix with the convolutions thereof spaced apart, said ribbon being coated substantially throughout its length with an electron emissive material.

22. A cathode for an electrical discharge device comprising a ribbon channel-shaped in section transverse to its longitudinal axis, said channel-shaped ribbon being formed in the shape of a helix with the convolutions thereof spaced apart, said ribbon being adapted to be heated to a temperature of appreciable thermionic emission. 1

23. A cathode for an electrical discharge device comprising a ribbon channel-shaped in section transverse to its longitudinal axis, said channel-shaped ribbon being formed in the shape of a spiral with the convolutions spaced apart.

ERWIN F. IDWRY, 

